1. Field of the Invention:
The present invention relates, in general, to combustion engines and, more specifically, to a cranking fuel control method and apparatus for reducing the emissions of particulates and gases from the engine during starting.
2. Description of the Prior Art:
Fuel injection systems have been designed for use in many different types of internal combustion engines, particularly, diesel engines, to improve the cold startability of such engines. Such systems operate by injecting relatively large amounts of fuel immediately upon the start of engine cranking into the engine. For example, in a diesel engine, the quantity of fuel injected during cranking is usually close to or in excess of the amount of fuel injected into the combustion chamber(s) of the engine at full operating load of the engine.
However, such fuel injection systems have many deficiencies caused by the fuel injected during cranking and starting of the engine. Such problems are related to the emission of high amounts of unburned hydrocarbons or fuel, liquid and solid particulates, and white smoke from the engine. Other problems are related to an increase in wear as a result of the dilution of the lubricating oil with the fuel, and in some engines, due to the high peak combustion gas pressures reached upon combustion after misfiring at the relatively low rotating speeds and the lack of formation of a lubricating oil film between the interacting surfaces of the engine components.
Many devices and methods have been devised to alleviate the problem of starting combustion engines, particularly on off-specification fuels or under cold ambient conditions. For example, in diesel engines some of these approaches include the use of compression ratios higher than the optimum compression ratio for a particular engine, the use of a glow plug in indirect injection engines, the use of air pre-heaters, and the injection of excessive amounts of fuel during cranking. All of these approaches enhance the formation of a combustible mixture of fuel-vapor and air at a temperature high enough to produce ignition and the subsequent combustion oxidation reactions. The oxidation reactions should release the energy required to produce work needed to overcome the engine frictional losses and accelerate the engine from the cranking speed to the idling speed.
The fuel injected during cranking may be ignited near the end of the first compression stroke following the start of cranking. In the case of misfiring during cranking, the injected fuel may go in any, or in a combination of routes: (a) accumulated in the cylinder and burned during the subsequent cycle or cycles; (b) discharged with the exhaust gases and deposited on the surfaces of the exhaust system; (c) emitted from the engine in the form of unburned hydrocarbon vapor or fuel, or in the form of liquid particulates appearing as white smoke, or (d) reaching the cylinder walls and leaking between the piston and cylinder to the crankcase. The fuel which is accumulated and burned during subsequent cycle(s) may result in spikes of high cylinder gas pressure and cause increased engine wear particularly at the relatively low cranking and starting speeds. The unburned fuel which is discharged from the cylinder results in an increase in the undesirable particulate and hydrocarbon or unburned fuel emissions from the engine. The fuel which leaks to the crankcase may dilute the lubricating oil and increase friction and wear in the engine.
Thus, it would be desirable to provide a method and apparatus for controlling the injection of fuel into various types of combustion engines during cranking of the engine which overcomes the aforementioned problems. It would also be desirable to provide a method and apparatus for controlling the injection of fuel during cranking of a combustion engine which can be easily installed in any new engine or retro-fitted onto any existing engine without undue modification of the engine. Finally, it would be desirable to provide a method and apparatus for controlling the injection of fuel during cranking of a combustion engine which can be implemented internally or externally in many types of mechanical or electronic fuel injection systems without adding additional devices or apparatus.